Mechanized slot drilling

ABSTRACT

A system and method are provided for providing access to surfaces within a formation is provided, the method including: providing a wellbore from a first surface location to a second surface location; inserting into the wellbore a cylindrical cutting assembly connected to at least two wellbore tubulars, one of the wellbore tubular extending to each of the first surface location and the second surface location; and rotating the radial cylindrical cutting element.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/866,400 filed Aug. 15, 2013, which is incorporated herein byreference.

FIELD OF THE INVENTION

The inventions relates to systems and methods for providing planeopening in formations.

BACKGROUND TO THE INVENTION

Considerable amounts of natural gas have been found to be produciblefrom formations such as source rocks, shale, and other low porosity andpermeability formations by drilling long horizontal wells andstimulating the wells with multiple propped fractures so that a largevolume of formation within a short distance of the well is connected tothe wellbore. Hydrocarbons trapped in such formations then migratetoward the volume connected to the wellbore at rates that can result ineconomic production of the hydrocarbons from formations that werepreviously considered to be uneconomic to produce. Although fracturingof the formations can result in profitable production, it would bedesirable to have an alternative to fracturing, to provide volumesconnected to wellbores within these formations.

U.S. Pat. No. 7,647,967 to Coleman et al. suggests a method to removemass from a formation between two connected wellbores by using aflexible cutting cable such as a segmented diamond cutting saw that ispulled reciprocally between two wellbores. The wellbores are drilled andconnected so that the cutting cable may be inserted into one of the two,and then fished from connecting wellbore, and then repeatedly pulledback and forth, removing formation between the wellbores to form anopening in the shape of a plane.

U.S. Pat. Nos. 4,232,904 and 5,033,795 suggest methods to removeminerals such as coal from seams using a chain cutter that is pulledthrough the seam initially from a tunnel drilled either in a U-shape orfrom two sides from which access to the seam is provided by excavationor from the seam outcropping.

Patent application publications WO2010/074980, WO2012/052496 and US2011/0247810 suggest variations of using a chain cutter pulled back andforth between wellbores for the purpose of hydrocarbon production.

Each of the references suggesting using flexible cutting cables rely onenergy transferred from rigs on the surface by lifting or reciprocatingthe cutters to provide energy, by lateral side force, for cutting theslot in the formation. The net energy that can be transmitted to cuttingformation is limited by the strengths of the cutting cables and thespeed with which surface rigs are able to reciprocate the cuttingcables. The result is that formation is removed at a relatively slowrate.

SPE paper 68441 by Philip Head et al. describes an electric coiledtubing drilling system that utilizes a fit for purpose electric motor todrive a steerable drill bit. Typically, steerable motors are driven byhydraulic positive displacement motors that utilize energy from pressureof the drilling fluid. With the electric drilling motor, drilling fluidproperties and flow rates are not constrained by the requirements ofboth the formation and drilling

SUMMARY OF THE INVENTION

A system is provided for providing access to surfaces within a formationcomprising: a cylindrical cutting assembly having a first end and asecond end: a cutting element positioned radially around a circumferenceof the cylindrical cutting assembly; a means for rotating the cuttingelement around the cutting assembly; and a means for moving the cuttingassembly through a wellbore wherein the cutting assembly is biasedagainst one side of the wellbore.

A method is also provide for providing a slotted opening in a formation,the method comprising: providing a wellbore from a first surfacelocation to a second surface location; inserting into the wellbore acylindrical cutting assembly connected to at least two wellbore tubular,one of the wellbore tubulars extending to each of the first surfacelocation and the second surface location; and rotating the radialcylindrical cutting element.

A system that may be used to accomplish this method is also provided,the apparatus comprising: a cylindrical cutting assembly having a firstend and a second end: a cutting element positioned radially around acircumference of the cylindrical cutting assembly; a means for torotating the cutting element around the cutting assembly; and a meansfor moving the cutting assembly through a wellbore wherein the cuttingassembly is biased against one side of the wellbore.

The method and apparatus of the present invention may provide moreenergy to be converted to mechanical motion within the wellbore toenable more rapid creation of slot volume than a system that requiresmechanical motion be provided from the surface facilities byreciprocating a cutting element.

This rotating cutting action may be provided from the electric motorswithin the wellbores, or could be enhanced or replaced by rotating theentire drilling assembly up to the max torque allowed by the pipe havingstrength similar to wellbore tubular used in conventional directionaldrilling. Pipe rotation is induced to the entire drill string from therotary table of the rig and drilling trajectory is planned to maximizethe rotation (therefore resulting cutting action) while minimizing bendcurvature and concentration of torque and bending moment in the drillpipe assembly.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic figure of a wellbore connecting wellheads at twosurface locations with a horizontal U-shaped section.

FIG. 2 is a schematic figure of a wellbore connecting wellheads at twosurface locations with a horizontal U-shaped section where a portion ofthe formation between the parallel legs of the U-shaped section has beenremoved according to the present invention.

FIG. 3 is a schematic of the apparatus of the present inventionconnected at each end to a wellbore tubular.

FIG. 4 is a schematic of a wellbore from which a slot could be providedfrom a single wellbore in a formation.

FIG. 5 is a schematic of alternative embodiment of the presentinvention.

DETAILED DESCRIPTION

Referring now to FIG. 1, a wellbore 101 with a horizontal U-shapedsection 102 is shown. The wellbore has substantially vertical sections103 extending from surface locations 104 where drilling rigs 105 areplaced. The vertical sections extend through overburden 106 and into atarget formation 107 that could contain hydrocarbons such as, forexample, natural gas. The sections of the wellbores that extend throughthe overburden may be cased with casings 108 that are cemented intoplace. The U-shaped section 102 preferably has two essentially parallellegs 109, connected by an essentially horizontal run 110. In someembodiments, the legs 109 could be tilted up, so that any hydrocarbonliquids produced from the wellbore after the well is completed wouldflow down to a point close to the vertical sections where they could beproduced, by for example, an electrical submersible pump. Tilting up ofthe legs 109 may also facilitate the removal of cuttings as the slot isformed since the circulating drilling fluid would tend to follow theshortest path between legs 109 which would be at the lowest point as theslot is formed and the cuttings would also tend to aggregate at thatlowest point. In other embodiments, the legs 109 could be angled up ordown so that the completed slotted wellbore could be sheared byhorizontal formation stresses to help maintain the slot open.

Wellbores 101 are shown with sections 103 being essentially vertical,but they could enter the overburden angled, for example, at 45 degreesfrom vertical. Having the wellbores start out at an angle would reducethe friction between the formation and tubulars moving within thewellbore caused by the greater change in the direction of the wellboreto transition to a more horizontal orientation. The optimum angle of thewellbore entering from the surface could be estimated as a trade-offbetween the change in frictional forces and the increased length ofvertical section 103 needed to reach the target formation 107.

Most formations contain a direction in which most naturally occurringfractures occur. The U-shaped wellbore could be placed so that thisplane, 111, is essentially perpendicular to the longest dimension of thefinished slot between the legs of the U-shaped wellbore. This wouldmaximize the number of natural fractures intersected, and increaseproduction of hydrocarbons from the finished wellbore.

The U-shaped wellbore could be, for example, constructed by starting twoseparate wells, and connecting the two wells by intersecting the twowellbores in the middle, at mid-point 112. It would be very difficult tohave the two wellbores lined up so that they intersect directly, but,for example, a magnetic device could be placed in the end of the firstof the two wellbores to be provided, and the second could bedirectionally drilled toward the magnet, and the wellbores could beconnected by intersecting the wellbores at a relatively small angle. Thechanges in direction shown in the figures are greatly exaggerated inorder to show the entire well, but could be provided with changes indirection in the range of 10 to 15 degrees for each one hundred feet ofthe wellbore. This is well within the range of directional drillingsystems used in the oil and gas industry.

Parallel legs 109, and essentially horizontal run 110 could be left asopen holes, or could be cased with a soft millable casing.

In another embodiment, parallel legs 109 could be placed in anessentially vertical plane and a vertical rather than a horizontal slotmay be formed.

The initial borehole is referred to as U-shaped, but the shape could besignificantly different. It is not intended that this description beliterally applied. For example, two wellbores could approach each otherat an angle rather than straight, and result in an initial borehole thatis the shape of a V instead of U, so long as the cutting element couldpass through the intersection of the wellbores.

The U-shaped well is drilled with conventional directional drillingtechniques. The dimensions of the U-shaped well may be, in general, withthe essentially parallel legs from 100 feet to two miles apart (31meters to 3250 meters), or, for example, 500 to 2000 feet apart (154meters to 615 meters). The total length of the U-shaped well is onlylimited by the distance the legs could be directionally drilled andintersected. With the total length of the U-shaped well limited, theratio of the distance between the essentially parallel legs and thelength of the essentially parallel legs may be between 1:1 and 5:1. Tarea of the final slot between the legs of the U-shaped section ismaximized when the ratio of the distance between the parallel legs andthe distance between the essentially parallel legs is 1:2. In otherembodiments, a longer length of the parallel legs may also be usefulbecause the resulting longer slotted well, if placed perpendicular tothe direction of naturally occurring fractures, would intersect morenaturally occurring fractures and therefore may more efficiently connectthe wellbores to a larger volume of the formation.

The two drilling rigs 105, when both are attached to the cuttingelement, would need to be operated in a coordinated manner. Adistributed control system (“DCS”) might be utilized to coordinate thisoperation and optionally allow operation of both drilling rigs by oneoperator. Non-rotating casing protectors (“NRDPP”) may also be utilizedto control wear of the casings and reduce torque and drag in sections ofthe wellbore not to be part of the slot to be created. NRDPPs aredescribed in, for example, SPE Paper 76759 by Fuller and Jardaneh, thedisclosure of which is incorporated herein by reference.

The motors could be hydraulic motors, and could be positive displacementhydraulic motors driven by a flow of drilling fluids. The motors couldalso be electrical motors such as the motor described in SPE paper 68441by Head et al., or electrical motors similar to motors used inelectrical submersible pumps. The motors may drive collars connected tocutting elements such as shearers similar to E-CTD type shearers,described in SPE paper 68441, SPE paper 52791 by Turner and et al, SPEpaper 46013 by Head and et al. The number of shearing elements driven byeach motor may be, for example, between one and one hundred, or betweenten and fifty. More than one motor could be incorporated in the system.Electrical power could be provided by cables such as those used to powerelectrical submersible pumps. The cables could be placed inside theconduits for protection, and here may be multiple cables or multiplecables extending to each surface rig. The total power that could beprovided to electrical motors for the present application could besufficient to provide, for example, 1000 horse power to drive cuttingelements. The motors described in SPE paper 68441 are claimed to becapable of producing up to 28 horsepower. Thirty or more of such motorscould be provided along a string of motor and cutting elements.

Typically, in a drilling operation, drilling fluids are circulated to adrill bit through a drilling string, and the drilling fluids cool andtransport rock cuttings back up the wellbore through an annular aroundthe drilling string. A system like this conventional drilling systemcould be used. Alternatively, drilling fluid could be pumped down onevertical wellbore, through the U-shaped portion and back up the otherwellbore. After the slot is at least partially created, the velocitiesof the drilling fluid may not be sufficient to remove all of thecuttings created. Cuttings remaining in the slot will not hindersubsequent hydrocarbon production because the slots will still havepermeability orders of magnitude higher than the formation.

Referring now to FIG. 2, the U-shaped wellbore 201 is shown with slots202 shown partially connecting two parallel legs, 203 and 204, of theU-shaped wellbore. The slot may be formed by placing in the well cuttingassemblies having motors driving cutting elements around thecircumference of the motors, and pulling the cutting element back andforth through the wellbore while tension is maintained on the cuttingelement by, for example, connecting each end of the cutting element todrill strings, coiled tubing, bars such as the bars used for sucker rodpumps, or combinations thereof. Multiple slots are shown in FIG. 2although in some embodiments, a single slot may be provided connectingessentially the full length of the parallel legs 203 and 204. Providingmultiple slots may reduce the cost by eliminating some slot cutting, andmay provide support and reduce the tendency of the slot to collapse.Instead of, or in addition to motors rotating the cutting assemblies,the cutting assemblies could be rotated from the surface. In general,coiled tubing could be advantageous because the operation could be morecontinuous and therefore proceed more rapidly.

Referring now to FIG. 3, a schematic drawing of a cutting assembly 301is shown. Cutting elements 302 are shown positioned radially around acircumference of the cutting assembly. A motor 303 within the cuttingassembly drives the cutting elements. End connections 304 connect theends of the cutting assembly to, for example, coiled tubing or drillstring elements 305, the coiled tubing or drill string may also providea protective conduit for electrical supply cables, and a path fordrilling fluids into the cutting assembly, so that the drilling fluidsmay be directed at the cutting elements to transport cuttings from thecutting elements. The cutting assembly could also include logginginstruments, or accelerometers to track the location of the cuttingassembly. Output from the logging tools and/or accelerometers could bemultiplexed and sent as a high frequency signal over the power supplycables to enable tracking of the progress of the operation.

The cutting assembly 301 could be assembled with high torque non-upsetconnections such as the TKC 4040 connection from Hunting EnergyServices, 1018 Rankin Road, Houston, Tex., 77049. The cutting elements302 could include wear resistant materials such as tungsten carbide,diamond impregnated elements or polycrystalline diamond cutters, and thecutting elements could be positioned along the length of the cuttingassembly. The cutting elements could be spiraled along the cylindricalouter surface of the cutting assembly. When hydraulic motors are used,fluids such as drilling mud could be provided from each of the drillingrigs, and, for example, an internal plug between motors being drivenfrom fluids coming from each direction could be provided. The cuttingassembly 301 could be provided with nozzles to distribute drillingfluids provide from one or both of the drilling rigs along the length ofthe cutting assembly as necessary to remove cuttings and to cool thecutting surfaces.

Joint 306 connects two separate motors 303, each of the two motorsdriving a separate set of cutting elements associated with that motor.The motors rotate the cutting elements in opposite directions, 307 and308, so that torque against the wall of the wellbore is counteracted bythe two oppositely turning sets of elements. Motor torque may also becounterbalanced, in some embodiments, by providing motors that turn inopposite directions.

Power supply is provided from surface facilities through cable 309.Commercially available power supplies useful, for example, forelectrical submersible pumps, may be utilized.

The cutting elements may be biased against one portion of the wellboreby being held in tension by, for example, drill strings, rods, or coiledtubing attached to each end of the cutting assembly.

Torque from the cutting elements against the wall of the borehole maycounter each other, by providing the cutting elements, or alternatingsets of cutting elements, that turn in alternating directions. Thiswould result in a more levelled and controllable slot being formed. Thecutting elements could be provided to turn in opposite directions byhaving, for example, alternating motors turning in opposite directions,or alternating motors could be geared to turn the cutting elements indifferent directions, or individual or sets of cutting elements could begeared to rotate in opposite directions.

In some embodiments of the present invention, the carrier pipe couldenhance or replace the cutting action from the electric motors byrotating the entire assembly up to the maximum torque capacity of thepipe, as currently done in directional drilling. In this embodiment,some or all of the cutting surfaces can be without a connection to amotor.

In some embodiments of the present invention, multiple horizontalU-shaped sections of wellbore could be provided from the same set ofvertical wellbores. The U-shaped sections of wellbore could be providedin opposite directions at similar levels, or multiple levels of U-shapedsections of wellbore could be provided at different elevations in thesame direction, or both. The U-shaped wellbores, and subsequent slottedwellbores, could be vertically displaced, for example, between 50 feet(15 meters) and 500 feet (154 meters), or between 70 feet (22 meters)and 200 feet (62 meters).

Now referring to FIG. 4, a vertical wellbore 401 with two horizontallegs, 402 and 403, are shown. The horizontal legs could be created byside-tracking from the vertical section in essentially the samedirection as a lower horizontal section, and drilling the side-trackedleg of the well to essentially horizontal, and then toward the lowersection to intersect the lower section. The lower section could havebeen drilled into an upward direction so that the intersection comes ata relatively small angle. This angle may be less than forty fivedegrees, or in another embodiment, between three and twenty degrees. Acutting element could then be placed in the wellbore according to thepresent invention and rotated or rotated and reciprocated to form a slotbetween the two horizontal legs. The horizontal legs may be legs thathave a horizontal component but extend outward from the wellbore 401 andthen connect to form a loop around a section of the formation 404 thatmay be removed by the present invention to form a slot. The slot may beessentially vertical. Multiple essentially vertical slots may be formedfrom a single wellbore by forming pairs of essentially horizontal legsin different directions. In one embodiment, there may be two pairs ofessentially horizontal legs provided in opposite directions, so that twoslots may be formed where both slots are essentially perpendicular tothe orientation of many naturally occurring fractures. In anotherembodiment, there may be, for example, four, six or eight pairs ofessentially horizontal legs extending from the wellbore to provide four,six, or eight slots in the formation extending from the essentiallyvertical wellbore.

Referring now to FIG. 5, an embodiment of the present invention is shownwhere two essentially parallel wellbores, 502 and 503, have beenconnected to form a section connecting the two parallel legs 504. Theessentially parallel wellbores could be vertical, horizontal, or betweenvertical and horizontal. Rotational power from the surface, or frommotors within the wellbores, is utilized to wind a cutting element 501around a pair of rotatable tubulars 504 and 506 and there byreciprocating the cutting element 501 between the two essentiallyparallel wellbores by rotating the tubular so that the cutting elementis wrapping around one tubular 506 as it is unwrapping from the otherrotatable tubular 505. After the cutting element is essentially unwoundfrom one rotatable tubular, the rotations are reversed and the cuttingelement is passed through the connecting section of the wellbore in theopposite direction. The rotatable tubular also maintains the cuttingelement in tension, and biased against the wall of the connectingsection of the wellbore so that the cutting element forms a slot in theformation between the two essentially parallel wellbores. Usingrotational power may reduce wear and abrasion experienced by tubulars505 and 506, and may reduce the tension on the cutting element. Thisembodiment may also eliminate a need to remove slack on the drill pipewhich would reduce non-productive rig time.

What is claimed is:
 1. A system for providing access to surfaces withina formation comprising: a cylindrical cutting assembly having a firstend and a second end: a cutting element positioned radially around acircumference of the cylindrical cutting assembly; a means for torotating the cutting element around the cutting assembly; and a meansfor moving the cutting assembly through a wellbore wherein the cuttingassembly is biased against one side of the wellbore.
 2. The system ofclaim 1 wherein the means for rotating the cylindrical cutting assemblycomprises a down-hole motor.
 3. The system of claim 1 wherein thedown-hole motor is an electrically powered motor.
 4. The system of claim2 wherein the system comprises a plurality of cylindrical cuttingelements.
 5. The system of claim 1 wherein the means for moving thecylindrical cutting assembly comprise connections on the first end andon the second end effective to couple the cutting assembly to wellboretubular.
 6. The system of claim 4 comprising a plurality of down-holemotors.
 7. The system of claim 1 wherein the cutting assembly is biasedagainst one side of the wellbore by the cutting assembly being held intension by wellbore tubulars connected to each of the first end and thesecond end of the cutting assembly, with the wellbore tubulars pullingthe cutting assembly against the one side of the wellbore.
 8. The systemof claim 4 wherein alternating sets of cutting elements are rotated inopposite directions
 9. The system of claim 3 where the down-hole motoris a hydraulic positive displacement motor.
 10. A method to provide aslotted opening within a formation, the method comprising the steps of:providing a wellbore from a first surface location to a second surfacelocation; inserting into the wellbore a cylindrical cutting assemblyconnected to at least two wellbore tubulars, one of the wellbore tubularextending to each of the first surface location and the second surfacelocation; and rotating the radial cylindrical cutting element.
 11. Themethod of claim 10 wherein the cylindrical cutting element is moved backand forth through the portion of the wellbore while the motor is drivingthe radial cutting elements.
 12. The method of claim 10 wherein theformation is a low permeability formation.
 13. The method of claim 12wherein the formation is a heavy oil containing formation
 14. The methodof claim 10 wherein the cylindrical cutting element is rotated by andown-hole electrically powered motor.
 15. The method of claim 10 whereinthe cylindrical cutting element is rotated by a hydraulic motor.
 16. Themethod of claim 15 wherein the hydraulic motor is a positivedisplacement motor.
 17. The method of claim 10 wherein the cylindricalcutting element is rotated by rotating from the surface the wellboretubular connected to the cylindrical cutting element.
 18. The method ofclaim 10 wherein the wellbore is comprised of predominantly verticalsegments extending down from each of the first surface location and thesecond location, and an essentially horizontal section between theessentially vertical sections.
 19. The method of claim 17 wherein thewellbore is further provided with essentially parallel horizontalsections extending from the bottom of the essentially vertical sections.20. The method of claim 10 wherein the slotted opening is placedessentially perpendicular to a plane of natural fractures within theformation.
 21. A method for providing a slotted opening in a formationcomprising: providing a wellbore within a formation having twoessentially parallel legs and a connecting section connecting the twoessentially parallel legs; providing a rotatable tubular in each of thetwo essentially parallel legs: passing a cutting element between the tworotatable tubulars through the connecting section of the wellbore bycausing the cutting element to wrap around one rotatable tubular as itis unwrapping from the other; and creating a slotted opening by biasingthe cutting element against the wall of the connecting section as it ispassing between the two rotatable tubular.